Working Fluid Selection and Performance Analysis for the Afyon Geothermal Energy Plant

Renewable energy production has been steadily increasing in recent years. Generating energy from renewable sources and making them operational for use is essential. Alongside production, efficiently utilizing these resources is equally important. For efficient use, exploring various alternatives and conducting optimization processes are crucial. Organic Rankine Cycles (ORCs) allow energy production from low enthalpy temperature sources. By using working fluids with low boiling points, it is possible to create a Rankine cycle at low temperatures. Each system operates under unique regional and environmental conditions, so careful selection of working fluids is necessary. Factors such as heat source temperature and pressure, ambient pressure and temperature, location, and purpose of use cause different fluids to exhibit varying behaviors. In this study, the effects of different working fluids were examined for the Afyon geothermal power plant. The active plant utilizes geothermal water at 110°C and a flow rate of 150 kg/s. The plant's capacity is approximately 2.7 MW. R-134a, a widely used working fluid, serves as the intermediary fluid. Additionally, fluids such as isopentane, n-pentane, isobutane, R-12, and R-32 were tested. Thermodynamic and thermoeconomic analyses of the system were conducted using these fluids. With R-134a, 2.75 MW of power was generated at a unit energy cost of $0.025/kWh. Among the alternative fluids, isobutane produced 2.95 MW of power with a unit energy cost of $0.016/kWh. The energy efficiencies of the system for R-134a and isobutane were 10.9% and 11.6%, respectively. Similarly, the exergy efficiencies for these fluids were 31.1% and 33.1%, respectively. Although better results can be achieved with certain alternative fluids, the data are insufficient to directly replace the current working fluid in the system. Performing a separate optimization study with these promising fluids will be a critical step in determining the final working fluid.